Gas doping systems for controlled doping of a melt of semiconductor or solar-grade material

ABSTRACT

A crystal pulling apparatus for producing an ingot is provided. The apparatus includes a furnace and a gas doping system. The furnace includes a crucible for holding a melt. The gas doping system includes a feeding tube, an evaporation receptacle, and a fluid flow restrictor. The feeding tube is positioned within the furnace, and includes at least one feeding tube sidewall, a first end through which a solid dopant is introduced into the feeding tube, and an opening opposite the first end through which a gaseous dopant is introduced into the furnace. The evaporation receptacle is configured to vaporize the dopant therein, and is disposed near the opening of the feeding tube. The fluid flow restrictor is configured to permit the passage of solid dopant therethrough and restrict the flow of gaseous dopant therethrough, and is disposed within the feeding tube between the first end and the evaporation receptacle.

FIELD

The field relates generally to preparation of single crystals ofsemiconductor or solar-grade material and, more specifically, to a gasdoping system for controlled doping of a melt of semiconductor orsolar-grade material.

BACKGROUND

Single crystal silicon, which is the starting material for mostprocesses for the fabrication of semiconductor electronic components, iscommonly prepared by the so-called Czochralski (“Cz”) method. In thismethod, polycrystalline silicon (“polysilicon”) is charged to a crucibleand melted, a seed crystal is brought into contact with the moltensilicon, and a single crystal is grown by slow extraction.

A certain amount of dopant is added to the melt to achieve a desiredresistivity in the silicon crystal. Conventionally, dopant is fed intothe melt from a feed hopper located a few feet above the silicon meltlevel. However, this approach is not favorable for volatile dopantsbecause such dopants tend to vaporize uncontrolled into the surroundingenvironment, resulting in the generation of oxide particles (i.e.,sub-oxides) that can fall into the melt and become incorporated into thegrowing crystal. These particles can act as heterogeneous nucleationsites, and ultimately result in failure of the crystal pulling process.

Further, in conventional systems, the sublimation of dopant granules atthe melt surface often causes a local temperature reduction of thesurrounding silicon melt, which in turn results in the formation of“silicon boats” adjacent the dopant granules. These silicon boats, alongwith the surface tension of the melt, prevent many of the dopantgranules that do reach the melt surface from sinking into the melt, thusincreasing the time during which sublimation to the atmosphere canoccur. This phenomenon results in a significant loss of dopant to thegaseous environment and further increases the concentration ofcontaminant particles in the growth chamber.

Some known dopant systems introduce volatile dopants into the growthchamber as a gas. However, such systems must be manually refilled eachtime a doping procedure is performed. Additionally, such systems cannotbe refilled while in use. As a result, such systems have a limiteddopant payload capacity for a single growth process. Such systems)therefore limit the size of silicon ingots that can be grown.Furthermore, such systems tend to supply dopant non-uniformly during agrowth process, thereby increasing the variation in dopant concentrationalong a grown ingot's longitudinal axis.

In other doping systems, inert gas is used to feed volatile dopants intoa growth chamber. However, the use of inert gas tends to dilute thegaseous dopant, thereby decreasing the dopant concentration, and purgethe evaporated dopant from the growth chamber too quickly. For example,dopants with low segregation coefficients such as arsenic (0.3) andphosphorus (0.35) require dopant concentrations in the melt of about 3times higher than the desired dopant concentration in the grown crystalto compensate. As a result, the evaporated dopant does not havesufficient time to diffuse into the silicon melt, and more) dopant isneeded to achieve a desired dopant concentration in the silicon melt.

Accordingly, a need exists for a simple, cost-effective approach toproduce low resistivity, doped single crystal silicon by the Czochralskimethod.

This Background section is intended to introduce the reader to variousaspects of art that may be related to various aspects of the presentdisclosure, which are described and/or claimed below. This discussion isbelieved to be helpful in providing the reader with backgroundinformation to facilitate a better understanding of the various aspectsof the present disclosure. Accordingly, it should be understood thatthese statements are to be read in this light, and not as admissions ofprior art.

BRIEF SUMMARY

In one aspect, a crystal pulling apparatus for producing a semiconductoror solar-grade ingot is provided. The apparatus includes a furnace and agas doping system. The furnace includes a crucible for holding a melt ofsemiconductor or solar-grade material. The gas doping system includes afeeding tube, an evaporation receptacle, and a fluid flow restrictor.The feeding tube is positioned within the furnace, and includes at leastone feeding tube sidewall, a first end through which a solid dopant isintroduced into the feeding tube, and an opening opposite the first endthrough which a gaseous dopant is introduced into the furnace. Theevaporation receptacle is configured to vaporize the dopant therein, andis disposed near the opening of the feeding tube. The fluid flowrestrictor is configured to permit the passage of solid dopanttherethrough and restrict the flow of gaseous dopant therethrough, andis disposed within the feeding tube between the first end and theevaporation receptacle.

In another aspect, a crystal pulling apparatus for producing asemiconductor or solar-grade ingot is provided. The apparatus includes afurnace and a gas doping system. The furnace includes a crucible forholding a melt of semiconductor or solar-grade material. The gas dopingsystem includes a feeding tube, an evaporation receptacle, and a fluidflow channel. The feeding tube is positioned within the furnace, andincludes at least one feeding tube sidewall, a first end through which asolid dopant is introduced into the feeding tube, and an openingopposite the first end through which a gaseous dopant is introduced intothe furnace. The evaporation receptacle is configured to vaporize thedopant therein, and is disposed near the opening of the feeding tube.The evaporation receptacle includes a base extending inwardly from afeeding tube sidewall, and a receptacle sidewall adjoining the base andextending upwardly from the base. The fluid flow channel is at leastpartially defined by the receptacle sidewall and a feeding tubesidewall.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is cross-section of a crystal pulling apparatus including a gasdoping system;

FIG. 2 is a cross-section of the gas doping system shown in FIG. 1 withvarious features omitted for illustration; and

FIG. 3 is a cross-section of an alternative gas doping system withvarious features omitted for illustration.

Like reference symbols used in the various drawings indicate likeelements.

DETAILED DESCRIPTION

A crystal pulling apparatus is indicated generally at 100 in FIG. 1. Thecrystal pulling apparatus 100 generally includes a crucible 102 forholding a melt 104 of semiconductor or solar-grade material, such assilicon, surrounded by a susceptor 106 contained within a furnace 108.The semiconductor or solar-grade material is melted by heat providedfrom one or more heating elements 110 surrounded by insulation 112.

A pulling mechanism 114 is provided within crystal pulling apparatus 100for growing and pulling ingots 116 out of the melt 104. Pullingmechanism 114 includes a pulling cable 118, a seed holder or chuck 120coupled to one end of pulling cable 118, and a seed crystal 122 coupledto the seed holder or chuck 120 for initiating crystal growth.

The crystal pulling apparatus 100 also includes a doping system(indicated generally at 130) for introducing gaseous dopant 132 into themelt 104. The doping system 130 includes a feeding tube 134, anevaporation receptacle 136, and a fluid flow restrictor 138. In thisembodiment, the gas doping system 130 also includes a dopant feedingdevice 140, a positioning system 142, and an inert gas supply 144.Generally, the gas doping system is configured to cause gaseous dopant132 to flow across a melt surface 146. Gaseous dopant 132 may beintroduced into furnace 108 before crystal growth commences and/orduring crystal growth, as shown in FIG. 1.

In operation, a solid volatile dopant 148, such as arsenic, phosphorous,or any other element or compound with a suitably low sublimation orevaporation temperature that enables the gas doping system to functionas described herein, is introduced into feeding tube 134 through a firstend 150 of feeding tube 134. Solid dopant 148 falls downwardly throughfeeding tube 134, and passes through fluid flow restrictor 138, and intoevaporation receptacle 136. Heat supplied to evaporation receptacle 136causes solid dopant 148 to vaporize into gaseous dopant 132. As gaseousdopant 132 expands, fluid flow restrictor 138 prevents gaseous dopant132 from flowing back through fluid flow restrictor 138 and into coolerparts of feeding tube 134 (“back flow”). An inert gas 152, supplied byinert gas supply 144, may be flowed through feeding tube 134 and throughfluid flow restrictor 138 to further restrict back flow of gaseousdopant 132. As gaseous dopant 132 vaporizes, it flows out of feedingtube 134 and across melt surface 146. As solid dopant 148 is consumed byvaporization, more solid dopant 148 may be fed into evaporationreceptacle 136 by feeding device 140. By continuously or intermittentlysupplying solid dopant 148 to evaporation receptacle 136, a relativelyconstant gaseous dopant 132 concentration can be maintained above themelt surface 146 during the doping process and the crystal growthprocess. Furthermore, compared to similar dopant feeding systems, fluidflow restrictor 138 reduces the amount of inert gas flow needed toprevent back flow of gaseous dopant, and/or to supply gaseous dopant tothe melt surface. As a result, the negative effects associated with theuse of inert gas flow in gas doping systems, e.g., dilution of gaseousdopant concentration and gaseous dopant being purged too rapidly fromthe furnace, are also reduced.

Referring now to FIG. 2, feeding tube 134 includes a feeding tubesidewall 154 having a first end 150 through which solid dopant 148 isintroduced, and an opening 156 opposite first end 150 through whichgaseous dopant 132 is introduced into furnace 108. In the embodimentshown in FIGS. 1 and 2, feeding tube 134 has a generally cylindricalshape defined by a single feeding tube sidewall 154 made of fusedquartz. In other embodiments, feeding tube 134 may have any othersuitable shape, and/or any number of feeding tube sidewalls that enablegas doping system 130 to function as described herein. In yet otherembodiments, feeding tube 134 may be made of tungsten, molybdenum, orany other suitably unreactive refractory material (including metals andceramics) that enables gas doping system 130 to function as describedherein.

Feeding tube 134 is positioned within furnace 108, and extends through avalve assembly 158 and outside of furnace 108. In the embodiment shownin FIG. 1, feeding tube 134 is slidingly coupled to positioning system142. Positioning system 142 is configured to raise and/or lower feedingtube 134. In the embodiment shown in FIG. 1, positioning system 142includes a rail 160, a coupling member 162, and a motor (not shown)configured to move coupling member 162 along rail 160. Rail 160 extendsin a direction substantially parallel to the longitudinal axis 164 offeeding tube 134. Coupling member 162 is slidingly coupled to rail 160,and affixed to feeding tube 134. Using positioning system 142, feedingtube 134 may be raised and lowered into and out of furnace 108. In otherembodiments, feeding tube 134 may be positioned wholly within furnace108, and/or may be permanently attached to furnace 108. In yet otherembodiments, feeding tube 134 may be positioned within and/or securedwithin or outside furnace 108 in any manner that enables gas dopingsystem 130 to function as described herein.

In the embodiment shown in FIGS. 1 and 2, feeding tube 134 is angledwith respect to melt surface 146 to facilitate the distribution ofgaseous dopant 132 across melt surface 146. In the embodiment shown inFIGS. 1 and 2, feeding tube 134 is angled such that the longitudinalaxis 164 of feeding tube 134 forms an angle of between about 45 degreesand about 75 degrees with respect to the melt surface 146. Opening 156may also be angled with respect to the longitudinal axis 164 of feedingtube 134 to facilitate the distribution of gaseous dopant 132 acrossmelt surface 146. For example, in the embodiment shown in FIGS. 1 and 2,opening 156 is angled such that opening 156 is substantially parallel tomelt surface 146, and angled at an angle of between about 45 degrees andabout 75 degrees with respect to longitudinal axis 164 of feeding tube134. In other embodiments, feeding tube 134 may be positionedsubstantially perpendicular to the melt surface 146 such thatlongitudinal axis 164 of feeding tube 134 forms an angle of about 90degrees with respect to the melt surface 146. In yet other embodiments,feeding tube 134 and/or opening 156 may have any other suitableconfiguration or orientation that enables gas doping system 130 tofunction as described herein.

In this embodiment, feeding tube 134 is communicatively coupled to aninert gas supply 144 to reduce the back flow of gaseous dopant 132. Aninert gas 152 may be introduced into feeding tube 134 from inert gassupply 144 at a given flow rate, such that inert gas 152 flowsdownwardly towards opening 156. As described in more detail below, fluidflow restrictor 138 reduces and/or eliminates the flow rate of inert gas152 needed to prevent the back flow of gaseous dopant 132, and to supplygaseous dopant 132 to the melt surface 146. For example, inert gas flowrates of less than about 10 normal-liters per minute, less than about 5normal-liters per minute, or even less than about 2 normal-liters perminute can be used with gas doping system 130 while maintaining asufficient supply of gaseous dopant to melt surface 146. In theembodiment shown in FIGS. 1 and 2, the inert gas 152 is argon, althoughany other suitable inert gas may be used that enables the gas dopingsystem 130 to function as described herein.

Feeding tube 134 of this embodiment is communicatively coupled to adopant feeding device 140 configured to feed solid dopant 148 intofeeding tube 134. In this embodiment, dopant feeding device 140 isautomated, though in other embodiments it may be manually operated, oronly partially automated. Feeding device 140 may be configured toautomatically feed solid dopant 148 into feeding tube 134 based upon oneor more user-defined parameters, and/or environment-specific parameters.For example, automated feeding device 140 may feed solid dopant 148 intofeeding tube 134 based upon any one or more of the following parameters:preset time(s) during a growth process, user defined interval(s), themass of solid dopant 148 within feeding tube 134 and/or evaporationreceptacle 136, a concentration of gaseous dopant 132 within feedingtube 134, evaporation receptacle 136, and/or furnace 108, and avolumetric or mass flow rate of gaseous dopant 132 and/or inert gas 152.The continuous and/or intermittent feeding of solid dopant 148 toevaporation receptacle 136 enables a relatively constant gaseous dopantconcentration to be maintained within furnace 108 during the crystalgrowth process, resulting in a more uniform dopant concentration profilein grown ingots.

Feeding device 140 of this embodiment is coupled to a controller 182configured to control the frequency and/or amount of dopant 148 beingfed into feeding tube 134 by feeding device 140. Controller 182 includesa processor 184 configured to send and receive signals to and fromcontroller 182 and/or feeding device 140 based on one or moreuser-defined parameters and/or environment-specific parameters. In thisembodiment, controller 182 includes a user interface 186 coupled toprocessor 182, and a sensor 188 coupled to processor 182. User interface186 is configured to receive user-defined parameters, and communicateuser-defined parameters to processor 184 and/or controller 182. Sensor188 is configured to receive and/or measure environment-specificparameters, and communicate such environment-specific parameters toprocessor 184 and/or controller 182.

Evaporation receptacle 136 is positioned within feeding tube 134 nearopening 156. Evaporation receptacle 136 is configured to vaporize dopanttherein. Specifically, evaporation receptacle is configured to holddopant 148 and transmit heat to dopant 148 such that dopant vaporizeswithin evaporation receptacle 136. In this embodiment, evaporationreceptacle 136 may be positioned sufficiently near melt 104 such thatradiant heat from melt 104 is sufficient to vaporize dopant 148 withinevaporation receptacle 136. For example, evaporation receptacle 136 maybe positioned between about 1 centimeter and about 15 centimeters abovemelt surface 146. In other embodiments, a separate heating element (notshown) may be used to supply heat to evaporation receptacle 136 tovaporize dopant 148 therein.

In the embodiment shown in FIGS. 1 and 2, evaporation receptacle 136includes a base 166 extending laterally inward from feeding tubesidewall 154, and a receptacle sidewall 168 adjoining base 166 andextending upwardly from base 166 along the longitudinal axis 164 offeeding tube. In alternative embodiments, evaporation receptacle 136 mayhave any other suitable configuration that enables gas doping system 130to function as described herein. In the embodiment shown in FIGS. 1-2,evaporation receptacle 136 and feeding tube 134 are made from a singlepiece of fused quartz. Integrating the evaporation receptacle within thefeeding tube may provide a relatively simple construction of the gasdoping system, and may reduce the overall size of the gas doping system.As a result, positioning the feeding tube and the evaporation receptaclewithin the furnace using a positioning system, such as positioningsystem 142, is made easier. In other embodiments, evaporation receptacle136 may be made of any suitable material that enables gas doping system130 to function as described herein. In yet other embodiments,evaporation receptacle 136 and feeding tube 134 may be fabricated asseparate components.

A fluid flow channel 170 of this embodiment is partially defined byreceptacle sidewall 168 and feeding tube sidewall 154. Fluid flowchannel 170 provides fluid communication between evaporation receptacle136 and opening 156 for gaseous dopant 132 being vaporized inevaporation receptacle 136. The cross-sectional area of fluid flowchannel 170 perpendicular to the longitudinal axis 164 of feeding tube134 may be adjusted in order to increase or decrease the flow rate ofgaseous dopant 132 passing therethrough. For example, thecross-sectional area of fluid flow channel 170 may be decreased byextending the length of base 166. Similarly, the length of fluid flowchannel 170 may be increased or decreased by varying the height ofreceptacle sidewall 168. By adjusting the cross-sectional area and orthe length of fluid-flow channel 170, the flow rate of gaseous dopant132 flowing out of feeding tube 134 may be optimized for maximum dopingefficiency.

Fluid flow restrictor 138 is positioned within feeding tube 134 betweenfirst end 150 and evaporation receptacle 136. Fluid flow restrictor 138is configured to permit the passage of solid dopant 148 therethrough,and also restrict the flow of gaseous dopant 132 therethrough. Fluidflow restrictor 138 therefore acts as a one-way valve for dopantssupplied to furnace 108 via gas doping system 130.

In the embodiment shown in FIGS. 1 and 2, fluid flow restrictor 138includes a bottom 172 having a second opening 174 therethrough, and aconical sidewall 176. Conical sidewall extends inwardly from feedingtube sidewall 154, and downwardly towards bottom 172. The fluid-dynamicproperties of fluid-flow restrictor 138 reduce or prevent back flow ofgaseous dopant 132 through second opening 174, while also permittingsolid dopant 148 to pass therethrough. In the embodiment shown in FIGS.1 and 2, conical sidewall 176 funnels solid dopant 148 through secondopening 174, and into evaporation receptacle 136. As dopant 148 isvaporized in evaporation receptacle 136, conical sidewall 176 divertsgaseous dopant 132 flowing upwards away from second opening 174, therebylimiting back flow of gaseous dopant 132. Additionally, conical sidewall176 directs inert gas 152 through second opening 174 (which has asmaller cross-section than feeding tube 134), creating a localized highpressure area of inert gas 152 near second opening 174, therebyrestricting back flow of gaseous dopant 132 therethough. Fluid flowrestrictor 138 thus reduces, or eliminates, the need to flow inert gasthrough feeding tube in order to prevent back flow of gaseous dopant,and/or to supply gaseous dopant to the melt surface. As a result, thenegative effects associated with the use of inert gas flow in gas dopingsystems, namely, dilution of gaseous dopant concentration and gaseousdopant being purged too rapidly from the furnace, are also reduced.

As described above, in the embodiments shown in FIGS. 1 and 2, fluidflow restrictor 138 includes a bottom 172 having a second opening 174therethrough, and a conical sidewall 176 extending inwardly from feedingtube sidewall 154. In alternative embodiments, fluid flow restrictor 138may have any suitable configuration that enables gas dopant system 130to function as described herein. In the embodiment shown in FIGS. 1 and2, fluid flow restrictor 138 and feeding tube 134 are made of a singlepiece of fused quartz. In other words, fluid flow restrictor 138 andfeeding tube 134 are of a one-piece construction. Integrating the fluidflow restrictor within the feeding tube may reduce the overall size ofthe gas doping system. This may facilitate positioning the feeding tubeand the fluid flow restrictor within the furnace using a positioningsystem, such as positioning system 142. In other embodiments, fluid flowrestrictor and feeding tube may be made separately, and may be made ofany suitable material that enables gas doping system 130 to function asdescribed herein.

Referring now to FIG. 3, gas doping system 130 includes afluid-distribution plate 178 configured to distribute gaseous dopant 132across melt surface 146. In the embodiment shown in FIG. 3,fluid-distribution plate 178 is coupled to feeding tube 134 at a secondend 180 distal from first end 150. In the embodiment shown in FIG. 3,fluid-distribution plate has a hemi-spherical shape. In alternativeembodiments, fluid-distribution plate may have a conical, rectangular,or square shape, or any other suitable shape that enables gas dopingsystem 130 to function as described herein.

As described above, gas doping systems of the present disclosure providean improvement over known doping systems. The gas doping systemincreases doping efficiency by reducing the need for inert gas flow toprevent back flow of gaseous dopant and to supply gaseous dopant to themelt surface. By reducing the need of inert gas flow, the gas dopingsystem reduces the negative effects associated with the use of inert gasflow in gas doping systems, namely, dilution of gaseous dopantconcentration and gaseous dopant being purged too rapidly from thefurnace. Gas doping systems of this disclosure may increase dopingefficiency by enabling a continuous or intermittent supply of soliddopant to the evaporation receptacle during the crystal growth process.By continuously or intermittently supplying solid dopant to theevaporation receptacle, a relatively constant gaseous dopantconcentration can be maintained within the furnace during the crystalgrowth process. Gas doping systems of this disclosure may increasedoping efficiency by providing an angled feeding tube, an angled openingand/or a fluid-distribution plate at the feeding tube end where gaseousdopant exits feeding tube. By providing an angled feeding tube, anangled opening, and/or a fluid-distribution plate, the distribution ofgaseous dopant across the melt surface may be optimized to permitmaximum doping of the melt for a given amount of dopant. For example,systems of this disclosure may enable growth of highly doped crystalswith arsenic or phosphorous concentrations as high as 10¹⁹ to 10²⁰atoms/cm³.

When introducing elements of the present invention or the embodiment(s)thereof, the articles “a”, “an”, “the” and “said” are intended to meanthat there are one or more of the elements. The terms “comprising”,“including” and “having” are intended to be inclusive and mean thatthere may be additional elements other than the listed elements.

As various changes could be made in the above constructions and methodswithout departing from the scope of the invention, it is intended thatall matter contained in the above description and shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense.

1. A crystal pulling apparatus for producing a semiconductor or solar-grade ingot, the apparatus comprising: a furnace including a crucible for holding a melt of semiconductor or solar-grade material; and a gas doping system for introducing a dopant into the furnace, the gas doping system including a feeding tube positioned within the furnace, the feeding tube including at least one feeding tube sidewall, a first end through which a solid dopant is introduced into the feeding tube, and an opening opposite the first end through which a gaseous dopant is introduced into the furnace; an evaporation receptacle configured to vaporize the dopant therein, the receptacle disposed near the opening of the feeding tube; and a fluid flow restrictor configured to permit the passage of solid dopant therethrough and restrict the flow of gaseous dopant therethrough, the fluid flow restrictor disposed within the feeding tube between the first end and the evaporation receptacle.
 2. The crystal pulling apparatus as set forth in claim 1 wherein the fluid flow restrictor includes a bottom having a second opening therethrough, and a second sidewall extending inwardly from a feeding tube sidewall towards the bottom.
 3. The crystal pulling apparatus as set forth in claim 2 wherein the fluid flow restrictor is configured to permit the passage of solid dopant through the second opening, and to restrict the flow of gaseous dopant through the second opening.
 4. The crystal pulling apparatus as set forth in claim 2 wherein the second sidewall includes a conically-shaped portion.
 5. The crystal pulling apparatus as set forth in claim 1 wherein the evaporation receptacle includes a base extending inwardly from a feeding tube sidewall and a receptacle sidewall adjoining the base and extending upwardly from the base.
 6. The crystal pulling apparatus as set forth in claim 5 wherein the gas doping system further includes a fluid flow channel at least partially defined by the receptacle sidewall and a feeding tube sidewall.
 7. The crystal pulling apparatus as set forth in claim 1 wherein the feeding tube is communicatively coupled to a dopant feeding device configured to feed solid dopant into the feeding tube.
 8. The crystal pulling apparatus as set forth in claim 1 wherein the feeding tube is communicatively coupled to an automated dopant feeding device configured to automatically feed solid dopants into the feeding tube.
 9. The crystal pulling apparatus as set forth in claim 1 wherein the gas doping system further includes a fluid-distribution plate coupled to the feeding tube at a second end distal from the first end.
 10. The crystal pulling apparatus as set forth in claim 1 wherein the feeding tube is slidingly coupled to a positioning system configured to raise and lower the feeding tube.
 11. The crystal pulling apparatus as set forth in claim 1 wherein the opening of the feeding tube is angled at an angle of between about 45 degrees and about 75 degrees with respect to a longitudinal axis of the feeding tube.
 12. The crystal pulling apparatus as set forth in claim 1 wherein the feeding tube is angled at an angle of between about 45 degrees and about 75 degrees with respect to a surface of the melt.
 13. The crystal pulling apparatus as set forth in claim 1 wherein the evaporation receptacle is positioned sufficiently near the melt such that radiant heat from the melt is sufficient to vaporize the dopant within the evaporation receptacle.
 14. The crystal pulling apparatus as set forth in claim 1 wherein the evaporation receptacle is positioned between about 1 centimeter and about 15 centimeters above a surface of the melt.
 15. The crystal pulling apparatus as set forth in claim 1 wherein the feeding tube is communicatively coupled to an inert gas supply.
 16. A method of using the crystal pulling apparatus as set forth in claim 15, the method comprising the steps of introducing a dopant through the first end of the feeding tube; vaporizing the dopant within the evaporation receptacle; and flowing an inert gas through the feeding tube at a flow rate of less than about 10 normal-liters per minute.
 17. A crystal pulling apparatus for producing a semiconductor or solar-grade ingot, the apparatus comprising: a furnace including a crucible for holding a melt of semiconductor or solar-grade material; a gas doping system for introducing a dopant into the furnace, the gas doping system including: a feeding tube positioned within the furnace, the feeding tube including at least one feeding tube sidewall, a first end through which a solid dopant is introduced into the feeding tube, and an opening opposite the first end through which a gaseous dopant is introduced into the furnace; an evaporation receptacle configured to vaporize the dopant therein, the receptacle disposed near the opening of the feeding tube, and including: a base extending inwardly from a feeding tube sidewall; and a receptacle sidewall adjoining the base and extending upwardly from the base; and a fluid flow channel at least partially defined by the receptacle sidewall and a feeding tube sidewall.
 18. The crystal pulling apparatus as set forth in claim 17 wherein the gas doping system further includes a fluid flow restrictor configured to permit the passage of solid dopant therethrough and restrict the flow of gaseous dopant therethrough, the fluid flow restrictor disposed within the feeding tube between the first end and the evaporation receptacle.
 19. The crystal pulling apparatus as set forth in claim 18 wherein the fluid flow restrictor includes a bottom having a second opening therethrough, and a second sidewall extending inwardly from a feeding tube sidewall towards the bottom.
 20. The crystal pulling apparatus as set forth in claim 19 wherein the fluid flow restrictor is configured to permit the passage of solid dopant through the second opening, and restrict the flow of gaseous dopant through the second opening.
 21. The crystal pulling apparatus as set forth in claim 19 wherein the second sidewall includes a conically-shaped portion.
 22. The crystal pulling apparatus as set forth in claim 17 wherein the feeding tube is communicatively coupled to a dopant feeding device configured to feed solid dopant into the feeding tube.
 23. The crystal pulling apparatus as set forth in claim 17 wherein the feeding tube is communicatively coupled to an automated dopant feeding device configured to automatically feed solid dopants into the feeding tube.
 24. The crystal pulling apparatus as set forth in claim 17 wherein the gas doping system further includes a fluid-distribution plate coupled to the feeding tube at a second end distal from the first end.
 25. The crystal pulling apparatus as set forth in claim 17 wherein the feeding tube is slidingly coupled to a positioning system configured to raise and lower the feeding tube.
 26. The crystal pulling apparatus as set forth in claim 17 wherein the opening of the feeding tube is angled at an angle of between about 45 degrees and about 75 degrees with respect to a longitudinal axis of the feeding tube.
 27. The crystal pulling apparatus as set forth in claim 17 wherein the feeding tube is angled at an angle of between about 45 degrees and about 75 degrees with respect to a surface of the melt.
 28. The crystal pulling apparatus as set forth in claim 17 wherein the evaporation receptacle is positioned sufficiently near the melt such that radiant heat from the melt is sufficient to vaporize the dopant within the evaporation receptacle.
 29. The crystal pulling apparatus as set forth in claim 17 wherein the evaporation receptacle is positioned between about 1 centimeter and about 15 centimeters above a surface of the melt. 